Compound compressor



y 1941- RQH. SWART 2,243,541

COMPOUND COMPRESSOR Fil edAug. 2, 1959 2 Sheets-Sheet 1 INVENTOR.

y 1941- R. H. SWART COMPOUND COMPRESSOR Filed Aug. 2, 1939 2 Sheets-Sheet 2 6 EEEEEEEEEEEEEEEEEEEZEEE3 INVENTOR.

Qm V v I! ATTO tice to employ two compressors.

Patented May 27, 1941 UNITED STATES T 10. FEE

COMPOUND COMPRESSOR Richard H. Swart, Beloit, Wis., assignor-to Gen- 7 eral Refrigeration Corporation, Beloit', Wis, a

corporation of Delaware 8 Claims.

The invention relates to. refrigeration compressors and has reference more particularly to a compound compressor for compressing gaseous refrigerant and the like in two or more'stages.

In refrigerating systems where the required evaporating temperatures are low as, for example, below zero on the Fahrenheit scale, diflicultieshave always been encountered with the conventional single stage compressor. In such compressors the' compression ratio is high and the effective displacement of the compressor is below that desired because of. leakage and: reexpansion of the gas'in the clearance spaces. The over-all efficiency is therefore'low. In addition the discharge temperatures are always high, due to the high compression ratioand this is conducive to'poor valve operation as well as decomposition of oil and refrigerant in some cases. In large installations it is common prac- However, in small systems using motors of from one-fourth to ten horse power thecost of installation and maintenance of two compressors is excessive. Accordingly, the invention contemplates improvements to .a standard multiple cylinder compressor to :71? ie a compound unit.

An object of the invention is to provide-a compound compressor as' above described wherein the compression ratio in all stages will be low with correspondingly high volumetric displacement and unusually low power consumption, and wherein the high pressuregas will 'be'discharged at relatively low temperatures.

Another object resides in the'provision of'a compound compressor which'will have particular application to low temperature" systems and which will eliminate the difliculties heretofore encountered in maintaining a. vacuum seal at the rotating shaft since the crank case pressure can be regulated to be above atmospheric at all times.

Another object of the invention is to provide a-multi-stage compressor wherein the gas'from the first stage and which is at an intermediate pressure is cooled to improve the efiiciency of the unit and which also hasthe desired elfect of lowering the temperature of the high pressure gas discharged from the second stage.

With these and various other objects in view, the invention mayconsist of'certain novel features of construction and operation as will be more fully described andparticularly pointed out in the specification, drawings and claims appended hereto, g

In the drawings which illustrate an embodiment of the device and'wherein like reference characters are used'to designate like parts- Figure 1 is a sectional view of a compound compressor constructed in accordance with the present invention;

Figure 2 is a fragmentary sectional view illustrating a modification embodying an oil return check valve; and

Figure 3 is a fragmentary sectional view illustrating the invention as applied to a compressor provided with pistons of the trunk type.

In the drawings, particularly Figure 1,- the compound compressor it) includes a crank case H and a cylinder portion l2 which provides vertically disposed'cylinders Hand [4. Said latter portion is provided on its exterior with heat radiating fins l5. Bearings it are located in the crank case for journalling the crank shaft indicated in its entirety by numeral I1 and which includes a crank portion I8 and a second crank portion l9 having a degree relation therewith. One end of the crank shaft l1 terminates short of a fixed seal 20, whereas, said other end 2!, whichprojects beyond the removable plate 22 ofthe crank case, is tapered for receiving the conventional fly wheel (not shown). Said end also receives the usual bellows seal 23 which seals this end of the rotating crank shaft with respect to the compressor so as to prevent escape of refrigerant gas from the crank case and to also prevent the entrance of air into said crank case.

The crank portion ill of the crank shaft is operatively connected by the connecting rod 24 with apiston 25 having reciprocating movement within cylinder I3 and which forms the low pressure stage of the present compound compressor. In asimilar manner crank portion l9 connects with piston 26'by means of connectingrod 21, said piston reciprocating within cylinder l4 and forming the high pressure stage of the present unit. The plate 28, which carries the inlet and outlet valves, respectively, for each cylinder is bolted to the cylinder portion of the compressor by bolts ZQWhiCh additionally hold in place the head 39 of the compressor. Said head is provided with an annular suction passage 3! which receives the low pressure or suction gas returning from the evaporator. Having communication with this annular passage in the head are inlet valves 32 for the low pressure cylinder l3'and inlet valves 33 for the high pressure cylinder M;

The outlet valve 34 for cylinder I3 is located within a chamber in the head 39 to which is connected the outlet pipe 35. Said pipe therefore receives the compressed gas from the first stage of the present compressor. The outlet valve 36 for cylinder 14 is located within a similar chamber having connection with pipe 31 which receives the high pressure gas, or, in other words, the gas which has been compressed to condensing pressure.

In accordance with the invention the refrigerant gas flowing through pipe 35 is cooled either by water, air, or both. Therefore, a part of this pipe is provided with cooling fins 38 and a jacket 48 may also be located in association with said pipe for conducting water in contact with the same to further cool the compressed gas flowing through said pipe. As shown in Figure 1, said gas is delivered to the interior of the crank case at 4 I The gas within the crank case can escape only through the passage 42 located in the wall of cylinder M and which passage: extends a shor distance above the top of piston 25 when said piston is in its lowermost position. When the piston is located in its lowermost position the gas in the crank case will flow into cylinder l4 and as a result of upward movement of said piston the gas is further compressed, to be eventually discharged at a high pressure through the outlet valve'35 into the tube 3?. At the end of tube '31 a condenser indicated in its entirety by numeral :13 is provided for condensing the refrigerant gas into its liquid form which is eventually delivered to the receiver 44;

Inthe compound compressor of Figure 1 it will be observed that refrigerant gas at suction pressure is drawn in by both cylinders as the piston-s of said cylinders move downwardly since each cylinder is provided with an inlet valve for said low pressure gas. In cylinder l3 this low pressure gas is compressed and delivered by the outlet valve 36 to the inter-cooler comprising the fins 38, which cool the gas by dissipating the heat to the air, and the water jacket 48 which removes heat, from the gas by bringing relatively cool water-in contact with pipe 35. In this form of the invention the'gas from the cylinder 13, which is at an intermediate pressure, is supplied to the crank case of the compressor and periodically removed therefrom by the pumping action of the high pressure stage comprising piston 25 operatingwithin cylinder [4. The gas within the crank case is therefore above atmospheric pressure at all times, which eliminates difficulties heretofore encountered in maintaining a vacuum seal between the rotating crank shaft and its compressor. Due to the pressure within the crank case no air will be drawn in and the'conventional shaft seal 23 will also prevent escape of refrigerant gas along the rotating crank shaft I'l.

When the piston 26 reaches the limit of its stroke in a downward direction the passage lZ is uncovered and gas at intermediate pressure will flow into the cylinder Hi. As described, said piston has already drawn into the cylinder a charge of low pressure gas through the inlet valve 33. This low pressure gas is accordingly compressed to intermediate pressure and which compression is done at the expenditure of no mechanical work, thereby efiecting a very important gain in over-all efficiency; On the upward stroke of the'pistoni t6 the gas within cylinder i4 is further compressed and discharged through valve 36 to the condenser as described.

gas at suction pressure is compressed to an intermediate pressure. The relatively small difference between the suction and discharge pressures of this first stage produces a high volumetric displacement therefor and which is at a relatively low temperature. The inter-cooler removes sufficient heat from the gas so as to prevent overheating of the compressor and as described serious diiliculties at the seal are eliminated by maintaining the crank case at a pressure above atmospheric. The compression ratio of the second stage is also low since the gas is compressed from an intermediate pressure to a condensing pressure. There is also a mechanical gain in this stage as a result of the admission to the cylinder of said intermediate pressure gas, which raises the charge in the cylinder to said intermediate pressure, and the temperature of the gas when discharged is relatively low as a result of the inter-cooler which removes considerable heat from the gas following its compression in the first stage.

In Figure 2 the intermediate pressure gas from the inter-cooler is delivered by the connection 45 and passage 46 directly to the high pressure cylinder l4 instead of being first delivered to the crank case of the compressor. This is desirable due to the fact that some compressors operate with a high oil level and with the design shown in Figure l'considerable oil may be carried along with thegas into the high pressure cylinder. The. modification of Figure 2 additionally includes an oil return check valve comprising a tubular body portion 41 having a valve seat 43 adapted to be closed by the ball valve 49. Said ball valve when not in contact with its seat will rest on the perforated'plate 59 yieldingly held against. a stop shoulder by the coil spring 5:. The oil return check valve allows an intermediate pressure to prevail within the crank case of the compressorand also permits oil removed from the intermediate pressure gas to be returned to said crank case. However, even though the oil may be highly agitated in the crank case, it is impossible for any oil to work past the check valve during operation of the compressor, and also upon starting up of ,the'compressor, oil will be held within the crank case since the crank pressure is reduced very gradually due to the fact that the check valve will close immediately upon the suction pressure being reduced.

In Figure 3 the features of the present inventiori have been applied to a compressor having pistons of the trunk type. In this type of compressor the crank case I H has the usual cylinder 'portionllZ providing a cylinder H3 forming a low pressure stage and a cylinder l M for the high pressure stage. The outlet valve i3 3. for the cylinder E3 is located within a chamber in the head I30 of'the compressor, which chamber has-connection with outlet tube I35, which receives the gas that has been compressed to an intermediate pressure. The structure is similar for the outlet valve I36 for cylinder I I4 which is located within a chamber in the head I33 of the compressor connecting with pipe l3? receiving the high pressure gas, orfin other words, the gas that has been compressed to condensing pressure.

In this form of the invention the low pressure suction gas is admitted to the cylinders byvalves located in the respective pistons. The'tube conducting the low pressure or suction gas from the evaporator and delivering the same to the compressor is indicated at I3! and it will-be observed that said tube has connection so as to deliver are so constructed as to be in communication at all times with the suction gas supply tubes I3I. Accordingly, as said" pistons move downwardly within their cylinder their respective inlet valves will be caused to admit a supply of suction'gas which is drawn in to fill the cylinders.

In cylinder I It the suction gas is compressed 'to an intermediate pressure, and which is dis charged through outlet valve I34 to tube I35. The intercooler including the fins I38 and the water jacket MI! lowers the temperature of this intermediate pressure gas flowing through I35 and as shown in'Figure 3 said cool gas is delivered to the high pressure cylinder'as at I55. This auxiliary inlet port is uncovered when the piston I26 approximately reaches the limit of its stroke in a downward direction and the charge of low pressure gas within said cylinder is thereupon initially compressed by the gas at intermediate pressure, which flows into and fills the cylinder; raisingthe pressure to that of said 3 intermediate gas. This is a clear gain in energy and is an important factor in over-all efiiciency of the present compound compressor. On the return stroke of the piston the charge is compressed to a condensing or discharge pressure and forced. through outlet valves I36, to 'be eventually delivered to the condenser and receiver for the liquid refrigerant.

In this formoi the invention the intermediate pressure gas from the intercooler is also conducted to the crank case of the compressor for the purpose of maintaining within the crank case a pressure which will be above atmospheric. The connection I56 includes the oil return check valve I57 embodying the same internal structure as the check Valve disclosed in connection with Figure 2. The purpose of the oil return check valve is to permit an intermediate pressure to prevail within the crank case of the compressor and also permit oil removed from the interrnediate pressure gas to be returned to the crank case. Also the check valve prevents oil from foaming out of the crank case and into the high pressure cylinder whenever the compressor is started.

The several advantages of the form of compressor shown in Figure 1 are likewise attained by the compound unit of Figure 3. Both cylinders operate on a relatively low ratio of compression and the volumetric displacement is therefore high. By cooling the gas at intermediate pressure sumcient heat is abstracted therefrom so as to maintain the high pressure gas at a relatively low discharge temperature. Also as a result of the connection to the crank case of the compressor a pressure is maintained in said crank case which is at all times above atmospheric, and any oil removed from the intermediate pressure gas can be returned although oil from the crank case is efiectively prevented from flowing in an opposite direction.

The invention is not to be limited to or by details of construction of the particular embodiment thereof illustrated by the drawings as various other forms of the device will of course be apparent to those skilled in the art'without departing from the spirit of the invention orthe scope of the claims. I

What is claimed is:

1. In a multi-stagecompressor, a pair of cyl.-

inders disposed side by side and each having a piston operating therein, one cylinder comprising the low pressure stage of the compressor and operating'to compress low pressure gas to an intermediate pressure, the other cylinder comprising thehigh pressure stage and having an'inlet valve for said low pressure gas and an auxiliary inlet port for admitting thereto said intermediate pressure gas, whereby both gases arecompressed by: said other cylinder to a high discharge pressure, said auxiliary inlet port cornprising 'a passage in the wall of said cylinder ,communicatingwith the crank case at its lower end and having its upper end positioned so that the portisuncovered at the end of the suction diate pressure gas .to'the crank case-of the comstroke, andmeans for conducting said intermepressor.

2. In a multi-stage compressor, a pair of cyl inders disposed side by side and each having a piston operating therein, one cylinder comprising the low pressure stage of the compressor and operating to compress low'pressure gas to an intermediate pressure, the other cylinder comprising the high pressure stage and having an inlet Valve for said low pressure gas and an auxiliary inlet port for admitting thereto said intermediate pressure gas, whereby both said gases are compressed by said other cylinder to a high discharge pressure, said auxiliary inlet port comprising a passage in the wall'of said cylinder communicating with the crank case at its lower end and having, its upper end positioned so that'the port is uncovered at the end of the suction stroke, means for conducting said intermediate pressure gas to the crank case of the compressor, and other means associated therewith for cooling said gas.

3. In a multi-stage compressor, a low pressure cylinder and a high pressure cylinder each having pistons operating therein, an inlet valve for each cylinder for admitting low pressure gas to each cylinder during the suction stroke of the piston operating therein and which is compressed to an intermediate pressure in said low pressure cylinder, outlet valves for the cylinders respectively, an auxiliary inlet port located in the high pressure cylinder and positioned so that the said port is uncovered at the end of the suction stroke, means conducting said intermediate pressure gas to said inlet port whereby said intermediate pressure gas is supplied to the high pressure cylinder after the same has drawn in a charge of low pressure gas, and whereby both charges are further compressed to a high pressure, means cooling said intermediate pressure gas, and means using said last mentioned gas to maintain a pressure within the crank case of the compressor.

4. In a compound compressor, a pair of cylinders each having a piston operating therein, an inlet port for each cylinder having communication with a source of low pressure gas for admitting said low pressure gas to its respective cylinder duringthe suction stroke of the piston operating therein, an outlet valve for each cylinder, the said outlet valve for one of said cylinders discharging said gas at an intermediate pressure, an auxiliary inlet port located in the other cylinder and positioned so that the port is uncovered when the piston of its cylinder reaches the limit of its suction stroke, and means connecting the outlet valve of said first mentioned cylinder with said inlet port whereby gas at an intermediate pressure is supplied by said inlet port to the otherinlet port located in said other cylinder and positioned So that the port is uncovered when the piston of its cylinder reaches the limit of its suction stroke, means connecting the said inlet port with the outlet valve of the first mentioned cylinder whereby gas at an intermediate pressure is supplied by said inlet port to said other cylinder and is compressed along with a charge of low pressure gas, and other means for cooling the intermediate pressure gas while the same is being conducted from its outlet valve to the inlet port.

6. In a multi-stage compressor, a pair of cylinders disposed side by side and each having a piston operating therein, one cylinder comprising the low pressure stage of the compressor and having an inlet valve for admitting low pressure gas and an outlet valve for discharging said gas at an intermediate pressure, the other cylinder comprising the high pressure stage and also having an inlet valve for admitting low pressure gas and an outlet valve for delivering gas at the final discharge pressure, an auxiliary inlet port associated with said high pressure cylinder for admitting to said cylinder at the end of the suction stroke the intermediate pressure gas from said low pressure cylinder, whereby a charge of low pressure gas and a charge of said intermediate pressure gas are compressed in the high pressure cylinder to the final discharge pressure of the compressor, and means for cooling the intermediate pressure gas before the same is delivered to said high pressure cylinder. 7

'7. In a multi-stage compressor, a pair of cylinders dis-posed side by side and each having a piston operating therein, one cylinder comprising the low pressure stage of the compressor and having an inlet valve for admitting low pressure gas and an outlet valve for discharging said gas at an intermediate pressure, the other cylinder comprising the high pressure stage and also having an inlet valve for admitting low pressure gas and an outlet valve for delivering gas at the final discharge pressure, an auxiliary inlet port associated with said high pressure cylinder for -admitting to said cylinder at the end of the suction stroke the intermediate pressure gas from said low pressure cylinder, whereby a charge of low pressure gas and a charge of said intermediate pressure gas are compressed in the high pressure cylinder to the final discharge pressure of the compressor, and means constructed and arranged to maintain a pressure within the crank case of the compressor approximating said intermediate pressure.

8. In a multi-stage compressor, a pair of cylinders disposed side by side and each having a piston operating therein, one cylinder comprising the low pressure stage of the compressor and having an inlet port for admitting low pressure gas and an outlet valve for discharging said gas at an intermediate pressure, the other cylinder comprising the high pressure stage and also having an inlet valve for admitting low pressure gas and an outlet valve for delivering gas at the final discharge pressure, an auxiliary inlet port associated with said high pressure cylinder for admitting to said cylinder at the end of the suction stroke the intermediate pressure gas from said low pressure cylinder, whereby a charge of low pressure gas and a charge of said intermediate pressure gas are compressed in the high pressure cylinder to the final discharge pressure of the compressor, a connection from said inlet port to the interior of the crankcase of the compressor whereby oil in said intermediate gas may drain to the crankcase, and a check valve in said connection permitting the oil to flow to the crankcase but preventing flow of oil in an opposite direction.

RICHARD H. SWART.

CERTIFICATE OF CORRECTION.

Patent No. 2,2L 5, L 1. May 27, 191 .1.

RICHARD H. SWART.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, second column, line 22, claim 1, strike out the words and syllable "stroke, and means for conducting said interme-" and insert the same after the word suction" in line 20, same olaim; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. 7

Signed and sealed this 8th day of July, A. D, 19 41.

7 Henry Van Arsdale, (Seal) Acting Commis sioner of Patents. 

